just an educated guess, here goes.
for the first example, i've seen such pictures too. what i remember
from the picture is, the patrol is walking towards the observer,
the fence is on the right of the patrol. the rifle is resting on
the left hip, the left hand grasping the barrel guard (don't know
the proper name for the part).
on and off, the soldiers will tuck on the fence, testing for any
breaks. he will be using his right hand. i reckon that would be his
master arm, hence (normally) his firing arm. this will make his
left arm the supporting arm.
in the event of any exchange of fire, the patrol will just need to
swing his rifle 'round to face the north, while bringing his right
hand to the pistol grip. since his method of carrying his rifle is
away from his body, hence his LBV/webbing, he will not have to
worry about his LBV/webbing entangling with his rifle, therefore
slowing his reaction time.
for the second part, don't know yet. need to think a bit.
